Tissue Injuries. Hematomas do not always occur as a result of accidental trauma to the tissues of the body. They also may happen after undergoing a medical or dental procedure. Any sort of surgical procedure that involves cutting through skin or blood vessels has the potential to result in hematomas. Examples of such procedures include medical biopsies, incision and drainage, tooth removal, and thousands of others that involve any bleeding. Hematomas may develop around the surgical procedure site because of the trauma that is caused to the nearby blood vessels and tissues. Sometimes medical injections such as immunizations, blood thinners, and nutrient replacement supplementation injections can cause the development of a hematoma.